Ethiopian Opals: Facts, Fears and Fairytales
Legend has it that Ethiopia’s Queen Sheba adorned herself with precious opal when she visited King Solomon in Jerusalem. The first known evidence of human use of opal dates back approximately 6,000 years (Gebremedhin, K 2014). In1939, archaeologist Dr. Louis Leakey uncovered opal artifacts in a cave in Nakuru, Kenya dating back to 4000 BC, according to Allan Eckert’s book The World of Opal. Theseopals were most likely from Ethiopia (www.opalsdownunder.com 2015).
In modern times, opal was discovered in Ethiopia in the early 1990s at Mezezo in the Shewa Province. Nodules of a reddish brown volcanic host rock were found containing orange, red- dish brown, or “chocolate” brown precious opal, a significant percentage of which was prone to cracking (Filin, S., Puzynin, A., 2009) (Figure 3).
In 2008, at Wegel Tena in Welo (aka Wollo) Province, large quantities of white and crystal precious opal and occasionally some black material were discovered; reports indicate it is “every bit as stable as the better known Australian opals” (Young, J. 2011) (Figure 4.).
In 2013 at the Stayish mine, Gashena, in Welo province, mostly dark gray and black opal, along with some white and crystal opal was discovered (Kiefert, L., Hardy, P. et al, 2014). This new material is reported to be stable and not hydrophanic (Kiefert, L., Hardy,
P. 2015; Weinberg, D. (2015) (Figure 5).
The Ethiopian artisanal mining industry employs more than one million people. The major types of gemstones found in Ethiopia include garnets, emeralds, rubies, and opals. Opal accounts for nearly 98 percent of the precious stone exports of the country (Bekele,K. 2014). The volume of opal production from Ethiopia has been enormous. Combined production for 2011 and 2012 are estimated at 40 tonnes (Bekele, K. 2013). Based on
a conservative 20% yield, this could have produced 40 million carats of cut opals.
Twenty-seven countries are reportedly buying Ethiopian opal with India, China and the United States the leading customers (Yonick,
D. (2011). One need only walk around a major international trade show to comprehend the overwhelming volume of cut Ethiopian opal now on the market, so much so that it dwarfs what is currently available from Australia (Figure 6). In fact, Ethiopia may now have overtaken Australia as the world leader in opal production.
In 2010, Australian opal miner Peter Blythe wrote: “At the possible wrath of some Australian opal lovers I dare to make this
statement. If this field is as extensive as it may well be, perhaps in the future, Australia could lose its dominance in the light opal market.
People in our industry must stop using the line ‘Australia produces 95% of the world’s opal’ This is simply no longer true” (Blythe, P. 2011). From the author’s experience, Ethiopian opals sell at steep discounts over Australian material of similar sizes and similar appearance. This equates to about 50% less in smaller sizes
of the cheapest goods up to as much as 90% less in larger and finer qualities. Most of the opals on offer at the Bangkok and Hong Kong September shows fell in the US$10-$50/carat price range, although material as low as $2/ carat and as high as $200/carat was available. Many of the best-quality Ethiopian opals “exhibit brilliance on a scale not seen since the early Andamooka, South Australian produc- tions,” wrote George Williams, JTV Senior Gemstone Buyer (Williams, G. 2011). Rare and truly exceptional pieces can sport Australian level price tags. Exhibiting in the Fine Gem Pavilion at Hong Kong AWE, A. Kleinman & Company offered a stunning piece at $650
per carat. An 100.11 carat Ethiopian opal was featured in an elaborate jewellery clip named “Paysage d’Opale” from the California Rêverie Collection by Van Cleef and Arpels, Place Vendôme, Paris (Cristol, A. 2016).
The sudden availability of unprecedented quantities of beautiful opal at prices far lower than what the market had come to expect has invigorated demand for opals around the world. This bounty is also quite evident in beads, a product rarely available in Australian goods, but now plentiful in Ethiopian material ranging from low-grade white opal to multi-color dyed beads (Figures 7, 8).
Historically, opal has been regarded as more fragile than most other gemstones (www.opalsdownunder.com.au 2016).
Being relatively soft compared to some other gems also means it can scratch quite easily. It is also known to be brittle causing it to chip quite easily upon only minor impact. But the most bothersome habit is opal’s tendency to spontaneously crack or “craze”. This dreaded phenomenon is encountered to a greater or lesser extent in opals from every source in the world with, in the author’s experience, the possible exception of Andamooka, South Australia (www.gia 2016).
Australian opal’s excellent reputation is due in great part to generally minimal cracking or crazing, as well as diligent producers
who eliminate problematic material, not allowing it to make it to market. With an over 100-year track record, Australian opals set the benchmark for the trade, a standard by which opals from all other sources are judged.
Early production of material from Mezezo in the Shewa province quickly gained popular- ity as the world’s first chocolate colored opal, but much of it had a bad habit of cracking and/ or crazing (Figure 3). News of this material’s tendency to self-destruct spread rapidly, and a general fear of Ethiopian opal was instilled in dealers around the world.
Attempts to stabilize Mezezo mate- rial even resulted in the issuing of patent #US20110126815 filed on Nov. 30, 2010.
This multi-stage process requires a full year to complete, and its effectiveness has never been documented (www.patentorg.com 2016). SSEF laboratory in Basel, Switzerland, examined two resin-treated nodules from Shewa in 2011, and one of them fell apart while it was in the lab’s possession (Krzemnicki, M., 2011).
In 2009, The Australian Gemmologist magazine reported a stability treatment technique for cabochon-cut Shewa
opals involving immersion in anhydrous ethanol in a pressure-tight vessel (autoclave), slowly heating to 80°C and maintaining at that temperature for about a week resulting in supercritical drying. In the second phase of the process, hydrated low- molecular weight
silica sols were introduced into the open pores of the opal conducted under pressures of 500 to 600 bar, (i.e. from 500 to 600 times ordinary atmospheric pressure) after a preliminary vacuum treatment of the samples (Filin, S., Puzynin, A., 2009).
and three oval cabochons of white opal from Australia (including one boulder opal) led to breakage of all samples” (Rondeau, B. et al. 2010). Preliminary tests from two respected gemological laboratories indicates opal from Wegel Tena, Wollo, is considerably tougher than Australian opal.
Mike Romanella, partner in Commercial Mineral Company, Scottsdale, Arizona, notes that although the Wollo opal does not have the 100 years of proven history that the Australian opal has, his two-year experience with the material has been positive. “We’ve seen little crazing in the tens of thousands of pieces we’ve worked with, and we’ve had no returns from our customers” (Yonick, D. 2011).
The last great concern is Ethiopian opals’ varying degree of hydrophane effect (the ability to absorb water) ranging from insignificant to dramatic (Figure 9). Material from Wollo is re- ported to gain from 0% weight when immersed in water with up to 50% in a few extreme cases
(Bekele, K. 2013). In the author’s experience, most of it is moderately hydrophane gaining from 5-15%.
Although there have been some reports of cracking as a result of repeated hydration and drying of Welo material, Stone Group Laboratories conducted rigorous testing and reports: “When many stones were immersed
and then left to dry repeatedly (12 times), there was no cracking or change from their original appearance. The laboratory subjected smaller stones to high heat in order to rapidly dehydrate water-soaked stones and found them to be stable even under these conditions” (Williams, G. 2011).
The hydrophane characteristic does cause concerns for consumers who unwittingly allow their hydrophane opals to come into contact with liquids other than pure water. In the author’s experience, oils of any type, perspiration included, can permanently reduce or even eliminate the beautiful play-of-color.
The hydrophane effect also presents the After treatment, a far lower susceptibility to cracking was reported in this Shewa mate- rial, though the editor did note: “Since there is no published standardized test to assess comparative opal-crazing susceptibility, it is difficult to quantitatively demonstrate that these cabochon specimens showed enhanced stability to crazing relative to untreated ex- amples of portions of the same material other than by subjective comparative experience” (Filin, S., Puzynin, A., 2009) Commenting on
this complex hi-tech procedure, it was reported in GIA’s Gems & Gemology, “A stabilization process has been developed to prevent crazing of Ethiopian opal (Filin and Puzynin, 2009), but in our experience this appears unnecessary for translucent opals from Wegel Tena” (Rondeau, B. et al. 2010).
Regarding the toughness issue, Bear Williams of Stone Group Laboratory said: “Widely sold as nice crystal, opal is also tough and stable enough to be treated with smoke and heat and not craze. After treatment, I dropped a smaller, round Wollo opal from seven feet onto a hard tile floor. Most opal, including Australian, would crack; even a diamond might cleave, but this thing bounced back without damage” (Yonick, D. 2011).
GIA has reported similar test results stating “We noticed by accident that Wegel Tena opals could sustain a fall from 1.5m onto a concrete floor with no visible damage, even under the microscope. Repetition of this test on five oval cabochons did not produce any sign of damage. The same experiment with five oval cabochons from the Mezezo deposit opportunity to easily introduce a variety of colored dyes into the structure of the opal resulting in some rather stunning artificial colors, including the coveted black. Vivid pinks, greens and blues are rather easy to spot; oranges and reds can be a bit trickier as they mimic fine naturally colored fire opal from Mexico and Brazil (Figure 10).
Natural black opal was discovered in 2013 at the Stayish mine, Gashena, in the Welo province (Figure 5). This material has a distinctly different appearance from Australian black opal and looks quite similar to the smoke-treated material from Welo. InColor Spring 2015 reported: “Preliminary testing at the Gübelin Gem Lab in Switzerland revealed that thus far this new material
shows no evidence of porosity, which would therefore exclude it from being categorized as hydrophane” (Kiefert, L., Hardy, P. 2015).
The hydrophane characteristic of Ethiopian opal is due to its internal structure. Typical non-hydrophane waterproof opal is composed of silica spheres orderly arranged in a tightly compacted fashion that does not allow water molecules to penetrate. In contrast, the silica spheres in hydrophane opals are unstructured and random providing ample space for water and other liquids to be absorbed (Figure 11).
Initial fears of crazing after repeated water immersion and drying cycles proved largely unfounded. GIA reported “There was no change in appearance (color, diaphaneity, crazing, or play-of-color) in the samples that were submitted to alternating periods of immersion in water.
One customer who wears her opal constantly complained that it became more transparent when she took a shower, swam, or otherwise put her hands in water. She recognized, however, that the opal always returned to its original appearance after some time (depending on the duration of immersion)—which is due to its hydrophane character” (Rondeau, B. et al. 2010).
Some in the trade have suggested re-categorizing hydrophane opal. Reporting for Rapaport magazine, Deborah Yonick wrote, “Wollo opal should be recognized as a new type because it can absorb or lose water, affecting transparency and play-of-color when wet, but recovering all its qualities when dry,” report researchers. They describe this new Ethiopian opal find as different from the opals of Shewa Province.
Laboratory testing of the Wollo opal revealed most specimens were resistant to crazing after repeatedly being immersed in water and dried out over a period of time. Not only are they stable, researchers say, they’re surprisingly tough (Yonick, D. 2011).
Testing for the hydrophane effect is a rather simple matter. GIA suggested, under a microscope “simply place a single drop of water on the surface and observe how the water drop interacts with the opal. After a few seconds of allowing the water to either evaporate or soak into the stone, reexamine the appearance. If the water is absorbed into the stone, that area’s refractive index will be slightly different, creating an optical aberration where the drop is placed and confirming that the stone is hydrophane” (Renfro, N. 2013). Another hydrophane opal test protocol affectionately named the KISS method is to simple to touch the opal to the tongue, the degree of absorbency can be roughly judged by just how strongly the stone adheres (Figure 12).
Opal expert and ICA member Francesco Mazzero of Opalinda raised an important point. This weight change could present a problem if one is dealing with a meticulous customs department who insist on weighing opals being imported. From personal experience, in August 2015 the author submitted several samples of Ethiopian opal to the GIA laboratory in Bangkok for examination with a check in weight of 23.57 carats.
The check out weight was 23.43 carats, and GIA required the author sign
a waiver acknowledging the 0.14 carat discrepancy before release.
The weight difference can be accounted for by the fact that August is mid-rainy season in Thailand so relative humidity is rather high. A few weeks in the air conditioned GIA lab atmosphere with a lower relative humidity induced a drying effect resulting in the weight loss. Shipping from a humid environment like Bangkok or Hong Kong to a dry climate like Madrid, Spain or Tucson, Arizona, could result in a significantly lower weight upon arrival, presenting potential problems if a customs dispute were to develop. Documenting this effect provides dealers with evidence they may one day find useful.
Mazzero insists on testing all the Ethiopian opals his company sells for the degree of hydrophane effect they exhibit, and has developed a seven-point scale for comparison.
Weighing the opal dry, it is then immersed in water for five minutes and re-weighed Figure 13) The hydrophane factor is calculated by:
wet weight minus dry weight, divided by the dry weight, times 100. For example, a 10.00 carat dry opal weighs 10.10 carat after five minutes of immersion. 10.10 minus 10.00 = 0.1 ÷ 10 X
100 = 1.
In addition to this measurement, Mazzero provides a lab report from Laboratoire Français de Gemmologie documenting the dry weight and the differing weight after immersion in water for five minutes. (Pers Com 2015)
Social media has become a powerful means of disseminating information, both facts and fairytales. In August of this year on the Facebook discussion group Scamologist,
with over 7,000 members (at the time), one of the moderators made the statement that “nearly all” Ethiopian opals are resin treated to stabilize them against cracking”.
As a former cutter of Australian opal,
I’ve had thousands of stones pass across my dopsticks. In the mid-90s I performed research on synthetic opals stabilized by plastic impregnation that was published in Gems & Gemology. (Gem News 1995)
When Welo opals first arrived in Bangkok, I acquired a small selection of rough and cut stones for my personal collection; I do not sell Ethiopian opal.
Being an opal cutter, I have paid close attention to the boom of availability at the Tucson, JCK Las Vegas, Bangkok and Hong Kong shows over the past several years. Armed with my somewhat experienced background, I suspected there was something seriously wrong with the Scamologist modera- tor’s statement, and challenged it. Much to my surprise, a prominent Australian opal dealer and industry leader chimed in on Scamologist to support the statement writing “most of it has been stabilised with clear polyurethane like materials” and “Most Ethiopian cut opal on the market is undoubtedly stabilised.”
Setting out to find evidence one way or another, I surveyed five dealers in Bangkok’s Jewelry Trade Center (JTC). None of them had any resin-treated “waterproof” opals available. I performed a sampling hydrophane test and the results of my rather limited survey were revealed at the 96th GIA Gem Gathering on August 19, 2015 in Bangkok.
The response on Scamologist was that my study group was too small, saying, “I know many of the traders at the major shows. They stabilise them.” It was suggested a more appropriate study group would have been 25 dealers at the Hong Kong and Tucson shows. Since the Tucson show was five months away, I proceeded to carry out “Survey Plus”, visiting over 40 sellers of Ethiopian opal at the September 2015 Bangkok and Hong Kong shows. In order to avoid any suggestion of bias, I enlisted former ICA Executive Director Barbara Wheat as overseer of the new and improved survey.
In order to “smoke” out the elusive resin-treated opals, we told each dealer we
had a major TV marketing company looking for large quantities of resin-treated waterproof Ethiopian hydrophane opal (which was actually true) and asked if they could supply us with any samples. Every dealer contacted stated that their Ethiopian hydrophane opals were
not waterproof and did indeed absorb water. While all were forthright in pointing out which material in their inventory was dyed, not one could provide us with even a single sample of a resin-treated opal. Indeed, none of them had even heard of such a treatment.
Spill the Wine
But back to the Scamologist. One comment was “Imagine if Mr. Bergman’s tests were conducted with red wine rather than water. What sort of a mess would he be showing in his results”? Grasping the thorn tree, I did
exactly as the Scamologista suggested, and, as I am a glutton for pain, added coffee, as well.
Three of the whitest polished Ethio- pian opals I could find were chosen for the experiment since the white base would best
contrast staining by wine and coffee. The opals were first weighed, immersed in water until fully saturated then re-weighed in order to determine their relative hydrophane effect.
One absorbed about 8% and the other two
14% and 15% of their original weight. The two opals with the greater hydrophane effect were chosen for the test, while the third was kept as a base-color matching control sample.
The opals were allowed to dry until they returned to their original weight, placed in red wine and espresso coffee, and left to absorb the wine and coffee until fully saturated. They were then allowed to dry until they returned to their original weights. There were no visible changes in either of the opals, which had fully absorbed either red wine or coffee (Figure 14).
In similar experiments using rough hydro- phane opal, I found that red wine was readily absorbed into material with high hydrophanity (27% weight gain) and the pigment remained after drying (Figure 15 a & b). Wine slightly tinted the surface, but did not change the body color of low-hydrophanity material (6% weight gain), leading me to believe particle size of the colouring compound may play a role. Polishing could be also responsible for creating a surface sealing effect that prevents larger coloring particles from penetrating while allowing small water molecules to saturate the stone. These seemingly contradictory differences between rough and cut material being colored, nor not colored by wine have also been reported by Terry Coldham (Per Comm) and require further investigation.
While the concept of resin treating Ethiopian hydrophane opal initially sounds like a good idea, in practical reality it has yielded unsatisfactory results. Probably the most important point was raised by the GIA, who concluded resin treatment is “unnecessary for translucent opals from Wegel Tena” (Rondeau et al. 2010).
Treatment detection by gemological laboratories is always a concern to both dealers and consumers. With the discovery of hydrophane opal in Ethiopia, the potential
for polyurethane, other resin or oil treatments has certainly increased. According to Shane McClure, the GIA’s Director of Identification Services, “GIA has seen some, but not many and I believe most of them were treated with oil” (Sturman, 2015).
I repeated the Ethiopian hydrophane opal resin treatment experiment on cut opals with a non-branded two-part polyurethane resin and a UV cure windscreen repair resin both available in Bangkok. The undesirable clouding developed in both cases and was quite severe with the non-branded two part polyurethane resin rendering the specimen unsalable (Figure 16).
Resin treatment is a concern when dealing with opals from any source, as it is an effective means of reducing the visibility of cracks.
In order to be able to fairly compare results, I chose a cracked Australian opal from my collection, purchased a similar size, shape and color Ethiopian hydrophane opal and
heated it to induce cracks. Both opals were then immersed in water for 24 hours. The Australian opal demonstrated no weight gain, while the Ethiopian hydrophane opal gained about 8%.
Both opals were then kept in a dry environment for 24 hours, with the Ethiopian hydrophane opal subsequently returning to its original weight.
Both opals were then placed in Opticon® Resin No. 224 fracture sealer and heated to 80°C for one hour, then placed in a vacuum to 27mm Hg. This cycle was repeated three times. The opals were then left in the Opticon for
24 hours, removed, cleaned with paper towels and immersed in the hardener solution for
10 minutes, removed and cleaned again with paper towels and left to “cure” for 24 hours before final examination.
The Australian opal showed a slightly noticeable decrease in visibility of the cracks with no change in play-of-color. The Ethiopian hydrophane opal showed a more distinct reduc- tion in visibility of the cracks, although they were still detectable upon close inspection.
There was also a greater than 50% reduction in play-of-color (Figure 17).
In addition to this undesirable effect, the Ethiopian hydrophane opal developed an
egg-shaped cloud in one half of the stone, as well as hundreds of small snowball-like puffy white inclusions dispersed throughout the stone, barely visible to the naked eye, but read- ily seen through 10X magnification (Figure 18).
Mikko Åström of M&A Gemological Instruments (which manufactures Raman, FTIR and UV-Vis-NIR spectrometers) provided the following information. (Per Comm).
“An important part of the system provided with each instrument is gemology-oriented software, including libraries of gem reference spectra. These libraries must be absolutely accurate, as many gemological laboratories and individual gemologists rely on them.
At M&A each sample inserted into the library is carefully tested with multiple instruments, and in cases where there is any deviation of the data compared to scientific publications, it is abandoned.
Visible spectrum laser Raman technology is often inconclusive due to photoluminescence caused by traces of uranium in opal that
masks any Raman peaks generated by polymers. However, FTIR is an effective tool for differentiating most natural opals from their synthetic counterparts. It can detect water
in natural opal, which is very uncommon in synthetics. It can also detect polymers used
in the manufacturing process of many synthetic opals for stabilizing the material. Similarly, the infrared transmission window of opal happens to be located conveniently at the area where absorption of many polymers, resins and other organic molecules can be detected.
M&A have been trying to find resin impregnated Wollo hydrophane opal from within the market for more than a year, for the purpose of inserting its spectrum into the FTIR-library.
This search process has included numerous gem shows around the world including Tucson, Basel and Hong Kong. The sourcing of dyed (artificially colored) hydrophane opal has not been difficult at all, but locating resin-impregnated samples has proved to so far be impossible.
After failing to find a suitable reference sample, M & A made the decision to buy some hydrophane opal and treat it themselves.
Rough hydrophane samples were purchased from a seller known to market Ethiopian mate- rial. The hydrophane nature of the sample to be treated was confirmed by water droplet test under a microscope (G&G Fall 2013, Nathan Renfro). The sample was cut into two pieces with pliers: one was treated with Hughes Associates Opticon-224 resin, while the other was left intact for reference.
The opal sample was immersed in resin for 6 days at slightly elevated temperature. No hardener was used. The treated stone was then cut free-form, with a faceting machine
in order to make sure any polymer related absorptions were recorded from the actual opal material itself and not from any surface contamination. Then another water drop-test was performed before acquiring the FTIR-
spectrum. The result revealed the sample had no characteristics of hydrophane nature anymore.”
At Tucson 2016, a reputable dealer in Ethiopian opal was identified as possibly selling resin treated material. Geoscience professor Veronica Poteat visited their booth and randomly selected 38 Ethiopian opals of varying qualities from the dealer’s stock for water absorption testing. After 20 minutes in water, all but one had gained weight, empirical proof that 37 out of 38 were definitely not resin treated.
Gemology is about verifiable scientific evidence, not unsubstantiated rumours and hearsay. Touching an opal to your tongue to demonstrate it is hydrophane and not waterproof resin treated is just as scien- tific as testing it with high-tech equipment. Whilst performing the tongue test, one of the opals stuck so strongly it was actually painful to remove. Under the oversight of
author and gemologist Antoinette Matlins, we purchased the opal Professor Poteat identified as not being absorbent, along with 6 others
of assorted sizes and qualities. Antoinette Matlins hand delivered them to Alberto Scarani of M&A Gemological Instruments Ltd. for advanced FTIR testing, who reported none showed any sign of resin treatment (Figure 19).
To quote Bear Williams of Stone Group Laboratories: “Once information is released on a large enough scale that is not confirmed with the rest of the gemological community and it turns out to be incorrect, steps have to be taken so that the confusion does not spread” (Bergman, J. 2016).
In this article, I hope I have demonstrated to a reasonable degree that the vast major- ity of cut Ethiopian opals on the market are undoubtedly not stabilized. Furthermore, there is overwhelming gemological evidence that they do not need to be stabilized. The widespread presence of polyurethane-resin stabilized Ethiopian hydrophane opal on the market appears to be a fairytale.
Consumer confidence is vital to both the short-term and long-term economic health of our trade. Proper disclosure of all treatments is critical to maintaining economic health.
Equally important is avoiding the spreading of unfounded fears of non-existent treatments. Industry leaders bear the responsibility to uphold the highest of ethical standards from both behind the showcase and in the media.
The huge production from Ethiopia has invigorated the opal trade around the world, and undoubtedly taken a chunk out of the Australian opal market share. George Williams, JTV Senior Gemstone Buyer wrote “I have bought and sold opals from all sources for
a long time and am thrilled with the variety of body colors, patterns, and especially the brilliance of colors that Welo opal displays. Many exhibit brilliance on a scale not seen since the early Andamooka, South Australian productions. Further, high-dome cabs are available that best show the beautiful play of color in opal (Williams, G. 2011).
Williams concluded: “Welo is as important to the opal business today as the Australian mines were in the previous
century. The cornucopia of opal varieties that can imitate Lightning Ridge, Coober Pedy, Andamooka, Mexico or Brazilian opal from this new discovery alone will continue to bring excitement back to this “Queen of Gems” for many years to come.”
Suggested Ethiopian Opal Consum- er Care Declaration
Most Ethiopian opals will readily absorb any liquids with which they come into contact. Avoid exposure to coffee, tea, wine, oils, perfumes, soaps, dishwashing water and other liquids that could cause permanent and irreversible discoloration. Bead bracelets and necklaces should always be worn over clothing to avoid absorbing perspiration. Do
not fear accidental situations such as dropping your opal into a washbasin, glass of wine or cup of coffee, or getting caught in the rain.
Absorption is not immediate and requires more time than a quick dip to take effect.
Should your opal accidentally be im- mersed in water for an extended period of time, remove it and place it in a safe and dry location. The time period for drying out can be minutes to more than a week and will vary depending on stone body type, size and
environmental conditions. Do not try and speed up the natural drying process by placing in an oven, under a hot light or hair dryer!
Like most gems, opal should be handled and cleaned with care. Never use a steamer or ultrasonic, keep away from harsh cleaning agents, avoid high temperatures or sudden
temperature changes. Only wiping with a clean and dry soft cloth is recommended.
Reference & Further Reading
Bekele, K. (2013) Report on Ethiopian Opal. ICA Newsletter, Nov. 2013.
Bekele, K. (2014) Ethiopia loses more than USD90 Million due to rough gemstones export. http://www.thereporterethiopia.com Accessed 22/11/2015.
Bergman, J. (2016) Tanzanite; Facts, Fears & Fakes. AGA www.accreditedgemologists.org. Accessed 09/01/2016.
Blythe, P. (2011) Ethiopian opal update. <http:// mineshaft.com.au> Accessed 22/11/2015
Cristol, A. (2016) Opal in French Jewellery. LGM, www.gemlabmarseille.com. Accessed 10/01/2016.
Filin, S., Puzynin, A., (2009) Prevention of crack- ing in Ethiopian opal. Australian Gemmologist, Vol. 23, No. 12, 2009, pp. 579–582.
Gebremedhin, K (2014) Who is benefitting from Ethiopia’s global brandname opals? www. ethiopiabservatory.com accessed 22/11/2015
Gem News (1995) Gem News, Gems & Gemology Summer 1995 p. 138
GIA.edu (2016) Opal Quality Factors. http:// www.gia.edu/opal-quality-factor Accessed 10/01/2016
Kiefert, L., Hardy, P. et al, (2014) New Deposit of Black Opal from Ethiopia. Gem News International, Gems & Gemology, Winter 2014, Vol. 50, No. 4 pp. 303-5
Kiefert, L., Hardy, P. (2015) The Mines of The New Black Opal from Ethiopia. InColor Spring 2015 Issue 28 pp. 61
Krzemnicki, M., (2011) SSEF FACETTE
International Issue No.18, Jan. 2011, pp 7.
Mazzero, F. (2015) Opalinda, Personal communication email. 26/09/2015
Opalsdownunder.com.au (2015), The History of Opal. Accessed 22/11/2015
Opalsdownunder.com.au (2016) Opal Facts & Myths. <http://www.opalsdownunder.com. au/learn-about-opals/introductory/opal-facts- myths Accessed 10/01/2016>
Patentorg.com (2016) Method of Stabilizing Opals. US 08490612 B2 Patent Summary www.patentorg.com. Accessed 10/01/2016
Rondeau, B. et al. (2010), Play-of-color opal from Wegel Tena, Wollo province, Ethiopia. Gems & Gemology Summer 2010 pp. 90-105
Renfro, N. (2013) A Useful Technique to Confirm the Hydrophane Nature of Opal. Lab Notes, Gems & Gemology, Fall 2013, Vol. 49, No. 3
Sturman, N. (2015). GIA Laboratory, Bangkok personal communication, email. 02/12/2015
Weinberg, D. (2015) Australia is no
longer the world’s only source of black opals.
<https://www.linkedin.com/pulse/australia- longer- worlds-only-source-black-opals-david- weinberg?trk=prof post&trkSplashRedir=true&f orceNoSplash=true> Accessed 22/11/2015
Williams, G. (2011) Ethiopian Hydrophane Opal.
www.jtv.com Accessed 10/01/2016
Yonick, D. (2011) Ethiopian Opal. Colored Gem- stone, Rapaport Magazine www.diamonds.net Accessed 22/11/2015
Young, J. (2011) Welo Ethiopia Opal,
www.mindat.org Accessed 22/11/2015